Fiber reinforced plastics (FRP) are composite materials including thermosetting resins such as unsaturated polyester resins, epoxy resins and polyimide resins, matrix resins of thermoplastic resins such as polyethylenes, polypropylenes, polyamides, polysulfones, polyethersulfones and polyether ether ketones, and fiber reinforcements such as carbon fibers, glass fibers and aramid fibers. These composite materials are molded, for example, from a prepreg, which is an intermediate product, produced by impregnating a reinforced fiber with a matrix resin through molding and processing steps including heating and pressurizing. In particular, composite materials using a carbon fiber as a reinforced fiber have been recently frequently used as members of aircraft, automobiles, etc. due to their lightness and excellent mechanical characteristics such as high strength.
Incidentally, in a situation in which the age of making use of hydrogen, a clean fuel instead of a hydrocarbon fuel, so-called a hydrogen energy society is coming, it is expected that lightening of the storage container of hydrogen is further demanded in consideration of easiness of handling. Further, for that purpose, it is considered that use of carbon fiber reinforced plastics is effective that are more excellent in specific strength than metal materials such as stainless steel and aluminum conventionally having been used. However, it is almost impossible to use the carbon fiber reinforced plastic fabricated in a conventional manner simply as a vessel for hydrogen since organic plastics are generally low in barrier properties, particularly have properties of easily passing hydrogen gas therethrough.
Hence, when a carbon fiber reinforced plastic is utilized, gas barrier properties, particularly hydrogen gas barrier properties should be imparted to the fiber by some methods. Conventionally, when carbon fiber reinforced plastics are used, for example, as a structural material for hydrogen tanks, a liner comprising a aluminum plate is affixed to a plastic, or an aluminum foil is affixed thereto to thereby have imparted hydrogen gas barrier properties thereto in many cases. However, these methods pose the problems of a bonded surface being peeled due to difference of the thermal expansion coefficient, etc., whereby practical applications are prevented. Instead of such methods, although the surface of a hydrogen tank is attempted to be covered with an organic film, this method decreases the hydrogen permeability to some extent, but sufficient hydrogen gas barrier properties for practical applications are not always obtained so far (e.g., Patent Document 1).
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2005-126651
On the other hand, recently, a gas barrier material of thermal resistance that is made of a clay mineral has been developed (see Patent Document 2). This material is a clay mineral such as silicate having a lamellar crystal structure, highly oriented in one direction, and is processed such that dense layers are bonded to each other with a small amount of an organic binder to be, for example, a flexible film having heat resistance and high gas barrier properties alone. Up to now, lamellar silicate (clay) served as a filler has been used in an additive form to improve the gas barrier performance of FRP. In addition, although its effect was identified to some extent, the amount of addition was limited since the moldability of the plastic itself is worsened. It is considered that the technology of Patent Document 2 is an epoch-making technology which finds that a film extremely improved in heat resistance and gas barrier properties is obtained when a clay mineral conventionally used as a filler is utilized as a film.
Patent Document 2: Japanese Unexamined Patent Application Publication No. 2006-188645
The present inventors have diligently studied to aim to develop a composite material having high gas barrier properties, particularly hydrogen gas barrier properties, conventionally not obtained, by organically binding the technology of Patent Document 2 above to the technology of the carbon fiber reinforced plastic, having led to the present invention.